Spic is required for the differentiation of metaphocyte progenitor cells

Metaphocytes are tissue-resident myeloid-like cells of non-hematopoietic origin in zebrafish barrier tissues. How metaphocytes acquire myeloid cell properties from non-hematopoietic precursors during the development remains unknown. Here we show that metaphocytes are in situ generated from local progenitors guided by the ETS transcription factor Spic. Tg(spic:EGFP) transgenic fish were found to label both metaphocytes and their progenitor cells. While spic is dispensable for the formation of the metaphocyte progenitors, it is required for the progenitors to differentiate into immature metaphocytes. To decipher the molecular basis underlying the developmental arrest of metaphocytes in spic mutants, we sorted the metaphocyte progenitor cells from the epidermis and gill of the mutants and siblings and performed bulk RNA-seq analysis. The data suggests that Spic orchestrates the development of metaphocytes by promoting the expression of myeloid-associated genes, either directly or indirectly through downstream transcription factors. Gene expression profiling analysis of bulk RNA-seq data for metaphocyte progenitor cells from the epidermis and gill of spic mutant fish and siblings